Aqueous hydroxylamine solution

ABSTRACT

An aqueous hydroxylamine solution containing hydroxylamine in an amount of 30 wt. % or more, which contains iron in an amount of not more than 10 ppb, metal components other than iron in an amount of not more than 5 ppb for each metal component and trans-1,2-diaminocyclohexane-N,N,N&#39;,N&#39;-tetraacetic acid in an amount of 0.0005 to 0.5 wt. % is obtained by distillation of a concentrated aqueous crude hydroxylamine solution using a specifically surface treated distilling apparatus.

FIELD OF THE INVENTION

This invention relates to a highly-concentrated and highly-purifiedaqueous solution of free hydroxylamine (which is not in the form of asalt). The invention particularly relates to a highly-concentratedaqueous hydroxylamine solution containing almost no metal components andhaving such high stability that the solution is advantageously used forprocessing or washing electronic devices.

BACKGROUND OF THE INVENTION

An aqueous hydroxylamine solution has been hitherto used, for instance,as a processing solution or detergent for producing electronic devices.In particular, a highly-concentrated and highly-purified aqueoushydroxylamine solution containing almost no impurities (particularly,metal components) has been recently required, for example, for washingvery small and highly-integrated electronic devices such assemiconductor IC chips.

Hydroxylamine (NH₂OH) is generally synthesized by a known method. In themethod, sodium bisulfite and sodium nitrite are reacted in an aqueousphase to prepare an aqueous solution of sodium hydroxylamine sulfonate,which is then hydrolyzed to obtain an aqueous hydroxylamine sulfatesolution. The obtained solution is neutralized with sodium hydroxide togive an aqueous free hydroxylamine solution.

Hydroxylamine normally takes the form of crystals at room temperature,and its melting and boiling points are 33° C. and 57° C. (at 20 mmHg),respectively. The crystals of hydroxylamine are known to be explosivewhen heated, and an aqueous hydroxylamine solution is also known to beso unstable that it is liable to rapidly decompose. For this reason, anaqueous solution of stable hydroxylamine salt is beforehand prepared,and the free hydroxylamine is produced when it is used in industry.Since this process is troublesome and inconvenient, it has been desiredto find out a stabilizing agent specifically effective for freehydroxylamine. Examples of the stabilizing agents hitherto having beenproposed include 8-hydroxyquinoline (Japanese Patent ProvisionalPublication No. 57-100908), 1,10-phenanthroline (Japanese PatentProvisional Publication No. 58-69841), bipyridine (Japanese PatentProvisional Publication No. 58-69842), thiocarboxylic acids (JapanesePatent Provisional Publication No. 58-69843) and quinoline (JapanesePatent Provisional Publication No. 58-69844). Further, WO 97/22549 andU.S. Pat. No. 5,783,161 teach thattrans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid effectivelystabilizes free hydroxylamine.

The already proposed stabilizing agents, however, are not fullyeffective when used in a normal manner. In addition, a prepared aqueoushydroxylamine solution generally contains impurities such as metalcomponents (e.g., iron, aluminum, alkali metals such as sodium andpotassium), which are originally contained in the starting materials orintroduced in the preparation process.

In order to prepare a highly-purified aqueous free hydroxylaminesolution suitable for processing or washing semiconductor devices,concentration and distillation by heating are indispensable. However,these treatments are liable to cause explosion, and hence it is verydifficult to safely distill the aqueous hydroxylamine solution (which isunstable and corrosive) keeping its distillate from contamination withimpurities.

SUMMARY OF THE INVENTION

The present invention provides a highly-concentrated and highly-purifiedaqueous (free) hydroxylamine solution which contains, in particular,almost no metal components such as iron. The invention also provides aprocess for safely and easily preparing the aqueous hydroxylaminesolution.

The inventors already found a stabilizing agent by which an aqueous freehydroxylamine solution is stabilized effectively enough to safelyconcentrate and distill by heating, which istrans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA). The CDTAmakes it easy to store and transport an aqueous free hydroxylaminesolution. Further, the CDTA makes it possible to safely produce andsupply a purified aqueous hydroxylamine solution containing sodium andpotassium in an amount of 30 to 100 ppb for each and iron in an amountof 50 to 100 ppb. However, the purity of this level is still notadvantageous for treating electronic devices. In order to further purifythe aqueous hydroxylamine solution, the solution must be furtherconcentrated and distilled by heating. Such severe distillationprocedure is not easy, because a distilling apparatus is easily corrodedby hydroxylamine to release new impurities.

The present inventors have further studied and finally discovered that ahighly-purified aqueous hydroxylamine solution can be obtained bydistilling an aqueous crude hydroxylamine solution (hereinafter,referred to as “crude solution”) in the presence of the specificstabilizing agent (trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraaceticacid) using a stainless steel-made distilling apparatus which preferablyhas equipment (e.g., spatter separator) for keeping spatters of theconcentrated solution from contaminating the resulting solution andwhich has an inside surface treated with an aqueous hydroxylamine saltso that the surface may not be corroded to release impurities. Thusprepared aqueous hydroxylamine solution is much more pure than the crudesolution, and therefore is suitable for the use in washing semiconductordevices.

The invention resides in an aqueous hydroxylamine solution containinghydroxylamine in an amount of not less than 30 weight %, which containsiron in an amount of not more than 10 ppb, metal components other thaniron in an amount of not more than 5 ppb for each metal component andtrans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid in an amount of0.0005 to 0.5 weight %.

The invention further resides in a process for the preparation of ahighly purified aqueous hydroxylamine solution, comprising the steps of:

heating in a vessel an aqueous crude hydroxylamine solution containing40 to 60 weight % of hydroxylamine and 15 to 200 ppb of iron, in thepresence of trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid inan amount of 0.0005 to 0.5 weight % based on the weight of the crudesolution, to distill water off and to give a concentrated aqueoushydroxylamine solution containing hydroxylamine in an amount of 70 to 95weight %; and

distilling the concentrated aqueous hydroxylamine solution to give anaqueous hydroxylamine distillate by means of a stainless steel-madedistilling apparatus of which inner surface has been previously treatedwith an aqueous hydroxylamine salt solution.

The preferred embodiments of the invention are as follows.

(1) The aqueous hydroxylamine solution, wherein the amount of iron isnot more than 5 ppb (more preferably, not more than 3 ppb).

(2) The aqueous hydroxylamine solution, wherein the amounts of sodiumand potassium are not more than 2 ppb (more preferably, not more than 1ppb) for each.

(3) The aqueous hydroxylamine solution, wherein the amounts of metalcomponents other than iron are not more than 2 ppb (more preferably, notmore than 1 ppb) for each.

(4) The distilling apparatus is equipped with a device for keeping adistilled aqueous hydroxylamine solution from contamination with theconcentrated solution which spatters in the vessel.

(5) The concentrated aqueous hydroxylamine solution is distilled, whilea portion of the concentrated aqueous hydroxylamine solution is takenout from the vessel.

(6) The concentrated aqueous hydroxylamine solution taken out from thevessel is mixed with a freshly supplied aqueous crude hydroxylaminesolution to give an aqueous mixture which is then supplied into thevessel.

(7) A portion of the concentrated aqueous hydroxylamine solution takenout from the vessel is wasted before the mixing.

(8) Trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid issupplemented to the aqueous hydroxylamine distillate.

BRIEF DESCRIPTION OF THE DRAWING

FIGURE is a flow sheet of a distilling apparatus advantageously used forpreparing a purified aqueous hydroxylamine solution of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The process for preparing an aqueous hydroxylamine solution of theinvention is described below by referring to the attached drawing.

The distilling apparatus shown in FIGURE is composed of a material tankA for storing the starting material (i.e., crude aqueous hydroxylaminesolution), a circulating pump B which continuously leads the startingmaterial from the tank A to a heater C and then to an evaporating can Dthrough a transferring line 1, a condenser E for cooling a purifiedhydroxylamine gas separated from spatters of the material and ledthrough a gas-transferring line 3 connecting to the upper part of theevaporating can D, a pressure-reducing line (vacuum pump) 5 connectingto the outlet line of the condenser E, and a product tank F for storingthe resultant purified aqueous hydroxylamine solution which is condensedfrom the vapor containing hydroxylamine gas and which is led through acondensed liquid-transferring line 4 connecting to the condenser E. Thepressure-reducing line (vacuum pump) 5 keeps the internal pressure ofthe apparatus (evaporating can D, gas-transferring line 3, condenser E)at a predetermined level. A circulating line 2 is connected to the lowerpart of the evaporating can D, and a distillation residue of theconcentrated solution in the evaporating can D is sent back to thestarting material by the pump B through the line 2. A blow line 6 isprovided between the pump B and the heater C, and a portion of thedistillation residue is removed through the blow line 6 so as to keepthe content of impurities at an allowed level.

The evaporating can D (the main part of the distilling apparatus) isequipped with a spatter separator (not shown) for keeping spatters ofthe concentrated solution from entering the resulting solution. Theevaporating can D is made of stainless steel, and its inside surface isbeforehand treated with an aqueous solution of hydroxylamine salt (e.g.,hydroxylamine sulfate, hydroxylamine phosphate, hydroxylamine chloride)so as not to be corroded when it is kept into contact with corrosivehydroxylamine. The anticorrosive treatment can be performed by heatingthe inside surface at an atmospheric pressure in the presence of anaqueous hydroxylamine solution salt (approx. 0.2 to 20 wt. %) at approx.50 to 200° C. for more than approx. 3 minutes.

The aqueous hydroxylamine solution of the invention can be preparedusing the distilling apparatus of Figure in the following manner.

First, the aqueous crude hydroxylamine solution (starting material) issupplied into the material tank A. The crude solution can be prepared bythe aforementioned known method. Generally, the crude solution containsnot small amounts of impurities of non-volatile metal components such asiron, aluminum, sodium, potassium and calcium. The contents ofhydroxylamine and iron in the starting material of the crude solutionare in the ranges of 40 to 60 wt. % and 15 to 200 ppb, respectively.Prior to distillation,trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA) is addedto the crude solution in an amount of 0.0005 to 0.5 wt. % based on theweight of the solution. CDTA stabilizes the crude solution to keephydroxylamine from decomposing.

The circulating pump B continuously sends the starting material (crudeaqueous hydroxylamine solution) to the heater C through the transferringline 1, and the solution is heated by the heater C. The heated solutionis then transferred to the evaporating can D, in which the pressure isbeforehand reduced by the pressure-reducing line (vacuum pump) 5 and thetransferred hydroxylamine solution is concentrated and distill byheating. When the solution is distilled under a reduced pressure, theliquid temperature is preferably kept as low as possible. The distillingconditions usually are in the range of 45 to 50° C./12 to 17 mmHg. Bythe distillation under that conditions, the solution is concentrated sothat the content of hydroxylamine can become in the range of 70 to 90wt. % (particularly 78 to 90 wt. %). Spatters of the solution splashingduring the concentration are separated by equipment such as a spatterseparator.

The concentrated solution gives vapor containing highly-purifiedhydroxylamine gas, in which impurities are decreased by separating thespatters. The aqueous hydroxylamine gas (distillate gas) is sent to thecondenser E through the gas-transferring line 3 connecting to the upperpart of the evaporating can D. Preferably, the inside surface of theapparatus including the gas-transferring line 3, where the distillateruns, is beforehand treated for making anticorrosive as described aboveor covered with anticorrosive material (e.g., polypropylene,polyethylene, polytetrafluoroethylene).

While the distillation is continuously performed, a residue of theconcentrated solution accumulates in the evaporating can D. The residuecontains impurities (metal components) in high contents, but it alsocontains the stabilizing agent. During the distillation, theconcentrated solution is preferably controlled so that the contents ofthe stabilizing agent and impurities (particularly, iron) may be kept inthe ranges of 0.0005 to 0.5 wt. % and less than approx. 5 ppm,respectively, based on the amount of the solution. For controlling theconcentration of the solution, the distillation is preferably carriedout while the residue is taken out. A portion of the residue is properlytaken out through the circulating line 2 (which connects to the lowerpart of the evaporating can D) and the blow line 6, so as to keephydroxylamine from decomposing and further to keep the amount ofaccumulated impurities at an allowed level. In order to effectivelyperform the distillation, the residue is mixed with a freshly suppliedaqueous crude hydroxylamine solution, and the obtained mixture is againconcentrated by heating. A portion of the residue may be removed beforeor after the residue is mixed with the freshly supplied crude solution,and then the remaining mixture may be concentrated by heating.

The highly-purified hydroxylamine gas is cooled and condensed in thecondenser E, and the produced aqueous solution is introduced through thecondensed liquid-transferring line 4 into the product tank F, in whichthe resulting solution is stored. The stabilizing agent,trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA) ispreferably supplemented to thus obtained solution.

The prepared highly-concentrated and highly-purified aqueoushydroxylamine solution of the invention contains hydroxylamine in anamount of not less than 30 wt. %. The content of iron is not more than10 ppb, preferably not more than 5 ppb, and more preferably not morethan 3 ppb. The contents of metal components other than iron are notmore than 5 ppb, preferably not more than 2 ppb, and more preferably notmore than 1 ppb, for each component. In particular, each content ofsodium and potassium is preferably not more than 2 ppb, and morepreferably not more than 1 ppb. The resulting purified aqueoushydroxylamine solution of the invention contains the stabilizing agentof trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid in an amountof 0.0005 to 0.5 wt. %.

The present invention is further described with the followingnon-restrictive working examples.

EXAMPLE 1

An aqueous hydroxylamine solution according to the invention wasprepared from the crude solution by means of the distilling apparatusshown in Figure. The conditions for the preparation process were asfollows.

(1) A spatter separator was provided to the evaporating can to separatespatters of the solution splashing during the concentration. Theevaporating can and the gas-transferring line (through which thedistillate gas runs) were made of stainless steel, and their insidesurfaces were beforehand treated with a hydroxylamine salt. For theanticorrosive treatment, the inside surfaces were heated at approx. 100°C. at atmospheric pressure for 8 hours in the presence of an aqueoushydroxylamine-sulfate solution (20 wt. %).

(2) The starting material was an aqueous crude hydroxylamine solution ofapprox. 50 wt. % containing trans1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (stabilizing agent) inan amount of 0.005 wt. % based on the weight of the solution.

(3) Into the distilling apparatus, the starting material wascontinuously supplied from the material tank A at a rate of 250 L/hour.The resulting highly-purified aqueous hydroxylamine solution wasproduced at a rate of 230 L/hour, while the hydroxylamine solutioncontaining a relatively high amount of impurities was taken out throughthe blow line at a rate of 20 L/hour.

(4) The conditions for distillation were controlled so that the liquidtemperature in the evaporating can would be kept in the range of 45 to50° C./12-17 mmHg.

Thus, an aqueous hydroxylamine solution of the invention containinghydroxylamine in the amount of approx. 50 wt. % was prepared. Thecontents of metal components in the prepared solution are set forth inTable 1. In Table 2, the contents of metal components in the startingmaterial (i.e., aqueous crude hydroxylamine solution) are also shown.

TABLE 1 (1) aqueous hydroylamine solution of the invention Metalcomponents in the solution (ppb) Al Ca Cr Cu Fe Pb Mg Mn Ni K Na Zn 0.60.2 0.9 0.2 1-3.1 <0.3 0.05 0.03 0.2 <0.3 <0.1 0.6 (2) crude aqueoushydroxylamine solution (starting material)

TABLE 2 Metal components in the solution (ppb) Al Ca Cr Cu Fe Pb Mg MnNi K Na Zn 65 5 8 <1 42 <1 3 <1 4 32 23 <1

The results in Table 1 indicate that the highly-purified aqueoushydroxylamine solution of the invention contains metal components(particularly iron, aluminum, and alkali metals such as sodium andpotassium) in remarkably reduced amounts, as compared with the startingaqueous crude hydroxylamine solution.

What is claimed is:
 1. An aqueous hydroxylamine solution containing hydroxylamine in an amount of not less than 30 weight %, which contains iron in an amount of not more than 10 ppb, metal components other than iron in an amount of not more than 5 ppb for each metal component and trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid in an amount of 0.0005 to 0.5 weight %.
 2. The aqueous hydroxylamine solution of claim 1, wherein the amount of iron is not more than 5 ppb.
 3. The aqueous hydroxylamine solution of claim 1, wherein the amount of iron is not more than 3 ppb.
 4. The aqueous hydroxylamine solution of claim 1, wherein each amount for sodium and potassium is not more than 2 ppb.
 5. The aqueous hydroxylamine solution of claim 1, wherein each amount for sodium and potassium is not more than 1 ppb.
 6. The aqueous hydroxylamine solution of claim 1, wherein the amounts of metal components other than iron are not more than 2 ppb for each.
 7. A process for the preparation of the aqueous hydroxylamine solution of claim 1, comprising the steps of: heating in a vessel an aqueous crude hydroxylamine solution containing 40 to 60 weight % of hydroxylamine and 15 to 200 ppb of iron, in the presence of trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid in an amount of 0.0005 to 0.5 weight % based on the weight of the crude solution, to distill water off to give a concentrated aqueous hydroxylamine solution containing hydroxylamine in an amount of 70 to 95 weight %; and distilling the concentrated aqueous hydroxylamine solution to give an aqueous hydroxylamine distillate by means of a stainless steel-made distilling apparatus of which the inner surface has been previously treated with an aqueous hydroxylamine salt solution.
 8. The process of claim 7, wherein the distilling apparatus is equipped with a device for keeping a distilled aqueous hydroxylamine solution from contamination with the concentrated solution which spatters in the vessel.
 9. The process of claim 7, wherein the concentrated aqueous hydroxylamine solution is distilled, while a portion of the concentrated aqueous hydroxylamine solution is taken out from the vessel.
 10. The process of claim 9, wherein the concentrated aqueous hydroxylamine solution taken out from the vessel is mixed with a freshly supplied aqueous crude hydroxylamine solution to give an aqueous mixture which is then supplied into the vessel.
 11. The process of claim 10, wherein a portion of the concentrated aqueous hydroxylamine solution taken out from the vessel is wasted before the mixing.
 12. The process of claim 7, wherein trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid is supplemented to the aqueous hydroxylamine distillate. 